llm: make Tool.Run return ToolOut

This is preliminary work towards
allowing tools to add additional information.
No functional changes (at least, that's the intent).
diff --git a/claudetool/think.go b/claudetool/think.go
index 9611150..4fe3513 100644
--- a/claudetool/think.go
+++ b/claudetool/think.go
@@ -34,6 +34,6 @@
 `
 )
 
-func thinkRun(ctx context.Context, m json.RawMessage) ([]llm.Content, error) {
-	return llm.TextContent("recorded"), nil
+func thinkRun(ctx context.Context, m json.RawMessage) llm.ToolOut {
+	return llm.ToolOut{LLMContent: llm.TextContent("recorded")}
 }